1. Field of the Invention
This invention relates to a novel anticorrosive pigment composition and an anticorrosive coating composition containing the same. More particularly, this invention relates to an anticorrosive pigment composition which is compatible with various coating vehicles, oily, solvent-type and aqueous, and exhibits remarkable anticorrosive effects.
2. Brief Description of the Prior Art
Anticorrosive pigments may be roughly classified into two categories, viz. (a) the conventional anti-corrosive pigments and (b) the newer relatively non-toxic anticorrosive pigments.
The most representative pigments of category (a) are red lead and zinc chromate. It is well known that these pigments exhibit remarkable rust-inhibitory effects but since they are rich in toxic metals, such as lead and chromium, these pigments present serious environmental problems. It is for this reason that there was a standing demand for low-toxicity or non-toxic anticorrosive pigments.
Many of the conventional anticorrosive pigments, such as zinc chromate, strontium chromate, red lead, basic lead chromate, lead suboxide, etc., have deep colors such as yellow, vermilion, black-gray, etc. and, therefore, a finish coat, if applied, must be applied in an increased film thickness or in an increased number of coats. To overcome this disadvantage, the advent of light-colored anticorrosive pigments have been awaited.
To meet this demand, development work on new anticorrosive pigments gained momentum and, as a result, several types of non-toxic or low-toxicity anticorrosive pigments of category (b) have emerged on the market. These pigments are either of the phosphoric acid type, such as zinc phosphate, calcium phosphate, etc., of the molybdic acid type, such as zinc molybdate etc., or of the boric acid type, such as barium metaborate etc.
However, compared with the earlier lead and chromate type pigments, these low-toxicity anticorrosive pigments have room for improvement in rust inhibitory effect.
The inventor of this invention made a thorough analysis of the disadvantages of these known low-toxicity anticorrosive pigments and a research for improving their relatively low rust inhibitory activity. As a result, it was found that a novel class of non-toxic anticorrosive pigments equivalent in rust-inhibitory effect to lead and chromate type pigments can be produced by subjecting anticorrosive pigments based on aluminum dihydrogen tripolyphosphate to adjustment of water solubles and chemical modification or subjecting zinc or boron compounds to chemical modification.
Furthermore, as described in Japanese Patent Application KOKAI 7806/1982, the inventor of this invention attempted to overcome the disadvantage of the conventional lead type anticorrosive pigments, namely their intense colors, and created new anticorrosive pigments having superior rust inhibitory activity and white or light colors by reacting aluminum dihydrogen triphosphate with lead compounds. However, these pigments were subsequently found to be not fully satisfactory in stability when incorporated in certain resin coating vehicles and stored.
However, it has been found that the addition of a chemically modified zinc compound resulted in a marked improvement in stability, thus broadening the scope of utility of these pigments to a remarkable extent.